Shotgun metagenomic sequencing allows researchers to sample all genes in all organisms present in a given complex sample. The method is used to  evaluate bacterial diversity and detect the abundance of microbes in various environments. Shotgun metagenomics also provides a means to study unculturable microorganisms that are otherwise difficult or impossible to analyze. With the ability to combine many samples in a single sequencing run and obtain high sequence coverage per sample, NGS-based metagenomic sequencing can detect very low abundance members of the microbial community that may be missed or are too expensive to identify using other methods.